Problem is right after starting engine the temp rapidly spikes way past 220. Replaced thermostat again. Same issue. Seems as though coolant is not circulating either due to airlock or busted water pump. Is it possible for a water pump to not circulate at all even though no leaks are observed?

Did you properly bleed all of the air out of the system? It can really be a pain sometimes getting all of it out.

How long does it take from cold does it take to heat past 220? Do the cooling fans come on?

Not sure I properly bled the system. Will try that. The temp reaches and goes beyond 220 in about 5 min. It does not hover at 220, but instead continues to rise. Fans turn on when over hot. I notice the upper rad hose is cool. Tells me no coolant flow. I took the serpentine belt off to rotate the pump pulley. It turns freely with no resistance.

One other observation. Immediately after starting the engine I see white smoke coming from the front (engine left?) exhaust manifold. I did a cylinder compression test and all are at ~180 psi. Also did a radiator pressure test. Held steady at 15 psi.

So maybe a crapped out water pump, maybe an air lock in the engine block, AND maybe a cracked head gasket?

So let me ask this. Instead of drilling a bleeder hole in the t-stat what if I were to remove the t-stat entirely. Then run the engine to hopefully remove any airlock present. Then go back and reinstall the t-stat? Of course I would only remove enough coolant to allow removal of the t-stat housing so as not to introduce any more air.

So here is my update. I removed the t-stat and cranked the engine. Right away I noticed coolant flowing across the filler neck. I could also finally feel the upper hose becoming hot. So seems the water pump is functioning.

But... temp gauge still steadily increased past 212. Also noticed a lot of white smoke billowing from the front exhaust manifold as well as from the tail pipe. Although I did a cylinder compression test and a radiator pressure test (both of which indicated no leaks) I think my issue here is a blown head gasket.

A failed lower intake manifold gasket is more likely. It's not as common on pre-95 engines, but it can happen. Blown head gaskets are few and far between on any 3800.

So I replaced the lower intake manifold a few weeks ago since I clearly noticed coolant leaking up around the junction of the throttle body and upper plenum. Maybe I did'nt torque the bolts down enough? Maybe I didn't seat the gaskets correctly before reassembling?

But lets say the white smoke from the front of the engine is a result of a leaking lower intake manifold gasket. It doesn't help to explain why the engine is still overheating so rapidly. Even when I can detect coolant circulating. Frustrating!

Also, was the UIM replaced when you replaced the lower gaskets? Same for the throttle body gasket?

Have you tried bringing it up to temperature with the cap off until the thermostat opens so it's not building pressure? This is typically how I do the first fill after a major drain.

I turned the engine off before it climbed into the red zone. It would have if I let it.No, but I removed the t-stat and left the rad cap off. I replaced the UIM plenum, which came with gaskets. I replaces the LIM gaskets but did not replace the lower intake manifold.Engine still overheated. I saw coolant moving past the filler neck, and also noticed the upper radiator hose was hot.

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